Scattering-Dominant Contrast Agents for Optical Coherence Tomography

We report a scattering-dominant agent that significantly enhances optical coherence tomography (OCT) imaging contrast. Unlike most other gold nanoparticle-based OCT agents, which are absorption-dominant and reduce imaging depth, our agent is based on gold nanocages, which exhibit a surface plasmon resonance (SPR) peak around 780 nm and a scattering cross-section that exceeds the absorption cross-section. The scattering-dominant gold nanocages act as nanosized mirrors that enhance backscattered OCT signals. The synthesis protocol for these nanocages is provided in detail. The optical properties of the gold nanocages were characterized using OCT imaging and further validated with integrating sphere measurements. OCT contrast enhancement was demonstrated through imaging of tissue phantoms containing embedded nanocages, as well as ex vivo imaging of mouse tissues and in vivo imaging of a mouse tumor following intravenous administration of PEGylated gold nanocages. To the best of our knowledge, this is the first demonstration of scattering-dominant OCT contrast agents utilizing structured gold nanocages.